The present invention relates an improved system and methodology for substantially increasing the light output of a polarized optical projection system through the recovery of optical energy of an unused polarization.
A liquid crystal display (hereafter xe2x80x9cLCDxe2x80x9d) is a known device used to control the transmission of polarized light energy. The LCD may be either clear or opaque, depending on the current applied to the LCD. Because of this functionality, projection systems commonly use an array containing numerous LCDs to form an image source. In particular, the projection system inputs high intensity, polarized light energy to the LCD array (also called an imager), which selectively transmits some of the inputted light energy to form a projection of a desired image. Because a single LCD is relatively small, numerous LCDs can be packed together into the array, thereby forming an imager that can produce a high resolution image.
As suggested above, a projection system must first polarize the light input to the LCD. However, light energy from a light source, such as a bulb, may have either p-polarization or s-polarization. Since this light input to the LCD imager must be in one orientation (i.e., either p-polarization or s-polarization), the LCD projector generally uses only half of the light energy from the light source. However, it is desirable in projection systems to maximize the brightness and intensity of the light output. In response, various methodologies have been developed to capture the light energy of unusable polarization, to convert the polarization of this captured light energy, and then to redirect the converted light energy toward the LCD imager. These known polarization recovery methodologies involve creating an expanded beam of light in which the unused portion of the light (of undesired polarity) is sent through a half-wave plate to change the polarization and then recombined with the original polarized beam. Unfortunately, the implementation of these known methodologies requires complex, bulky systems, which usually include 2-dimensional lense arrays and an array of polarization beam splitters. Furthermore, the known methodologies lose much of the light energy and, therefore, compromise the projector""s goal of producing a high intensity output. As a result, there exists a current need for a simple, low cost, and compact polarization recovery system that operates with high efficiency.
In response to these needs, the present invention uses a waveguide system to perform the polarization recovery function in an LCD projection system. In particular, the present invention""s waveguide polarization recovery system both polarizes the input light energy for use with an LCD imager and converts the polarity of unusable light energy to add to the illumination of the LCD imager. The compact polarization recovery waveguide system generally includes the following optical components that are integrated into a single unit: (1) an input waveguide that inputs non-polarized light energy into the system; (2) an output waveguide that removes polarized light energy from the system; (3) a polarized beam splitter that receives the light energy from the input waveguide and transmits light energy of a first polarization type and reflects light energy of a second polarization type, and (4) a wave plate that modifies the polarization of either the transmitted or reflected light energy. The polarization recovery system also generally includes one or more mirrors that are positioned as needed to direct the transmitted and/or reflected light energy to the output waveguide. The input and output waveguides may be shaped as needed by the projection system. For example, either one or both of the input and output waveguides may be tapered as needed to produce a desired image.
In the waveguide polarization recovery system, the input and output waveguides are configured to have either a substantially parallel or a substantially perpendicular orientation. In configurations in which the input and output waveguides are substantially parallel, the output waveguide directly receives light energy transmitted by the beam splitter. In this way, light energy enters and exits the polarization recovery system in substantially the same direction. Alternatively, the input and the output waveguides may be positioned substantially perpendicular to each other such that the light energy exits the polarization recovery system at a right angle from the direction it enters. In configurations having input and output waveguides of perpendicular orientation, a mirror receives the light energy transmitted by the polarized beam splitter and redirects this energy by 90xc2x0 toward the output waveguide.
The polarization recovery waveguide system of the present invention combines the above-enumerated list of optical components into a single, compact unit. In one embodiment, the waveguide polarization recovery system further includes one or more xe2x80x9cgapsxe2x80x9d of optically clear material positioned between the optical components to encourage the occurrence of total internal reflection that minimizes the loss of the optical energy by the system.